During machining operations, technicians typically locate a work piece relative to a tool, such as a laser, spindle operated tool, or a nozzle of a water-jet. Technicians may position a work piece relative to a known reference datum so that offsets may be calculated for positioning features such as holes, pockets, or cuts on the work piece. Often the features to be machined within the work piece will be generated in a Computer Aided Design (CAD) system, such as Pro/ENGINEER®, Unigraphics®, or CATIA®. When a CAD system is used, the locations of the features may be calculated within the software relative to the reference datum. To ensure that the features are machined in the proper place within the work piece, it is required to accurately locate the work piece relative to the reference datum. This is often done by the guess-and-check method where a technician may iteratively mark the work piece with a laser and then move one or the other accordingly until the laser strikes a desired portion of the work piece. The calibration may be repeated until the work piece is located in the proper position. Once properly positioned with respect to the reference datum, the CAD system can proceed to control the machining of the work piece. The calibration may be repeated periodically for production runs to ensure consistency and meet tolerances.
Although this iterative guess-and-check calibration method may be sufficient in locating a work piece, the method may not be ideal for production runs or where consistency is needed and efficiency is desired. When the work piece and machining tools are small, such as, for example, in laser machining applications, it may be required to remove a work piece between each iteration. The removal of the work piece may be required to locate the reference marks on the work piece using a microscope or other imaging device that can enlarge an image of the work piece.
An attempt at calibrating a laser welding system is described in U.S. Pat. No. 5,168,141 (the '141 patent) issued to Tashjian et al. The '141 patent discloses a laser welding system including a laser welder, a positioning table, and a camera. The positioning table is associated with a table coordinate system, and the camera is associated with a camera coordinate system for a field of view of the camera. A metal sheet is placed on the positioning table under the laser welder, and the laser welder emits a laser beam to burn a hole in the metal sheet at a position, corresponding to a predetermined focal point of the laser welder, on the table coordinate system. The camera records the position of the focal point according to the camera coordinate system and inputs the data to a computer. The computer instructs the positioning table to iteratively adjust the position of the metal sheet, according to an algorithm, until the focal point has the same coordinate on both the table coordinate system and the camera coordinate system, thereby calibrating the camera to the positioning table.
Although the laser welding method of the '141 patent provides a technique for iteratively calibrating a focal point location between a camera field of view and a positioning table, the method may be inefficient for laser machining applications because numerous guess-and-check iterations may be required for calibration.
The calibration method of the present disclosure solves one or more of the problems set forth above and/or other deficiencies in existing technology.